It is proposed to measure periodontal disease activity via quantification of certain by-products of bacterial metabolise in the infected pocket. It is known that an anaerobic environment provides a necessary condition for an active disease, but this condition may not be sufficient. Other relevant chemical conditions may involve the pH and concentrations of H2S and HS-. Hence, an "activity index", based on these concentrations, indicating the presence, and activity of the disease may be developed. The measurement will utilize a disposable dental probe tip containign electrodes capable of measuring p02, pH and [H2S]. The proposing organization's expertise is in microelectrode technology and it has existing sensors capable of these determinations. The proposed analytical techniques will be chronoamperometry and potentiometry controlled by micro-processor-based cirtuitry. The probe is to be placed in the infected pocket and rapidly (under 10 sec.) in real time, and simultaneously, the concentrations mentioned above will be determined, and electronically correlated into the "activity index". Phase I will be devoted to bhe development of a working probe prototype with preliminary clinical studies carried out in collaboration with Dr. R. G. Caffessee at the University of Texas. Production methodolgies, comprehensive clinical studies, and steps toward FDA approval will be the subject for a Phase II continuation.